Rotary vane pumps are often used in automotive vehicles for transferring hydraulic fluid to power steering, brakes, and transmission, as well as auxiliary systems such as supercharging, etc. Such pumps are variable displacement pumps and include multiple vanes mounted on a rotor that generally rotates inside a cavity. The center of the rotor is positioned eccentrically within the cavity—that is, the rotor is offset from the center of the cavity. The vanes are slidably mounted, so that they can slide radially in and out during rotation. The eccentric position of the rotor means that the walls of the cavity lie at a variable length from the rotor axis. Thus, the pump cells—the volume between adjacent vanes—can vary in volume during a rotation cycle.
When used in the automotive vehicles, the rotors are generally driven directly by the vehicle engine, and the quantity of hydraulic fluid delivered by these pumps varies in response to variations in the engine speed. When the engine speed is relatively high or low, a lift ring is generally provided to ensure an adequate delivery of the hydraulic fluid, and. The lift ring substantially surrounds the rotor, adjustable between different positions eccentric to the rotor. Specifically, the lift ring adjusts the quantity of the hydraulic fluid delivered in direct proportion to the engine speed, thus ensuring adequate delivery.
As the vanes rotate, variations in cell volume create alternating suction and pressure zones. As a cell passes from a suction zone to a pressure zone, a pressure pulse is produced on the delivery side of the pump, and this pulse may lead to undesired noises vibrations within and emanating from the pump.
Attempts have been conventionally made to reduce such vibrations or undesired noises. Some pumps are provided with odd number of vanes, or with control valves within certain openings, to alleviate this problem. Another approach employs V-shaped notches at certain suction and delivery openings. At some angular positions of the moving rotor, these notches form overflow channels between adjacent cells, as the cells transit from the suction zones to the pressure zones. These measures ameliorate the noise problem, but they is may significantly reduce delivery pressure, reducing the pump's effectiveness.
Accordingly, considering the problems noted above, there remains a need for an adjustable vane pump, which may substantially reduce pressure pulsations in the delivered hydraulic fluid, and decrease the noise due to vibrations within mechanical components of the pump, when the rotating vanes transition from the suction zone to the pressure zone within the pump.